Note:  For detailed or extended answers, it is recommended that you construct your responses in a document before entering them into the essay boxes on the quiz or test.

If for some reason you need to navigate away from the assignment, click the Finish Attempt button as shown below.  

After you click Finish Attempt, what you've typed is saved.  You get the next screen below, and you can navigate back to the home page of the course using the breadcrumb in the red box.
When you come back later to the assignment, the screen will look like the below picture and you can click Continue your attempt to pick up where you left off.